Wireless communications devices are an integral part of society and permeate daily life. The typical wireless communications device includes an antenna, and a transceiver coupled to the antenna. The transceiver and the antenna cooperate to transmit and receive communications signals. A typical radio frequency (RF) transceiver includes a power amplifier for amplifying low amplitude signals for transmission via the antenna.
One example of a wireless communications device is a high frequency (HF) wireless communications device. The typical HF wireless communications device covers the frequency range of 1.5-30 MHz and provides several benefits. For example, the HF wireless communications device offers potential worldwide communication capabilities with little to no infrastructure. Indeed, HF communication is popular with many amateur (HAM) radio operators, permitting one operator to readily contact another operator on another continent. The long range of HF wireless communication systems is to the result of the good propagation characteristics of HF waves reflecting off of and refracting with the Earth's ionosphere. Nevertheless, worldwide HF communication may only be available in the best of ionospheric conditions. Other conditions that may affect HF communications include, for example, sunlight/darkness at site of transmission and reception, season, solar sunspot cycle, solar activity, and polar aurora. Accordingly, the user may manually cycle through several frequencies to find a channel suitable for transmission.
Notwithstanding the above noted benefits of the HF wireless communications device, the typical HF wireless communications device may have a limited bandwidth of 3-5 KHz, for example. Attempts at expanding the typical bandwidth of the HF wireless communications device may suffer from several drawbacks. In particular, several components in the typical HF wireless communications device may be non-linear outside the typical operation bandwidth. For example, the coupler, which couples the antenna to the power amplifier by way of impedance transformation, may introduce distortion into the frequency spectrum of a wideband HF signal.
One approach to HF distortion is disclosed in U.S. Pat. No. 5,164,959 to Cai et al. Cai et al. discloses a HF communications device comprising receiver path with a correlator module for determining transmission channel characteristics. The HF communications device uses the determined transmission channel characteristics to generate a signal for transmission that reduces the transmission channel.